A new swine flu virus is infecting a growing number of people in the United States. But the official response to this outbreak is substantially different from the one that greeted the swine H1N1 virus that emerged in 2009.
Public health authorities, perhaps still stinging from criticism of the response to the H1N1 pandemic, are struggling to strike the right note with this virus, which so far doesn't seem to be spreading from person to person. But is their low-key strategy the right one to take?
One prominent flu expert is questioning the approach, which has largely focused on encouraging people not to eat or drink while touring pig barns at fairs and to wash their hands after visiting these exhibits.
Michael Osterholm suggests it's too soon to conclude that this new virus is going to be a mere nuisance or just another weird chapter in the ever-perplexing saga of influenza viruses.
And he says it's time to take what likely would be a very unpopular step — tell organizers that this year, pigs should stay home from the fair.
"I'm convinced that wherever you have pigs and fairs right now you're seeing this transmission —at least in North America," says Osterholm, director of the University of Minnesota's Center for Infectious Diseases Research and Policy, and of the Minnesota Center for Excellence in Influenza Research and Surveillance.
"These pigs shouldn't be at the fairs."
The virus, an influenza A of the H3N2 family and a distant cousin of human viruses of the same name, was first spotted in humans last summer. To distinguish between the animal and human viruses, scientists call this H3N2-variant or H3N2v.
(Following a sharp drop in pork sales, human health officials gave in to pressure from the agricultural lobby to stop using the term swine flu during the 2009 pandemic, so now swine-origin viruses are called variants when they infect people.)
Cases have predominantly cropped up among children who have attended agricultural exhibitions. But human health officials in the U.S. have been reluctant to call for the closure of pig barns this fair season.
Asked about the issue on a recent teleconference with the media, a senior influenza scientist with the Centers for Disease Control said a two-pronged strategy was being introduced to try to bring the situation at fairs under control.
The plan: Stress hand hygiene among humans and screen pigs at they arrive to weed out evidently unhealthy animals.
"So I don't think it's necessary at this point at least to cancel a swine show," Dr. Joe Bresee, the CDC's head of influenza epidemiology said on Aug. 9.
"We'll continue to follow these things, and we'll continue to follow the cases and learn more about the epidemiology and exposures of risks over the coming weeks. And the recommendations may change. But I think let's let the prevention strategies that are just now being put in place take hold and see what we get."
Just last week, however, a CDC journal published an article reporting that many seemingly healthy pigs that are brought to show in the United States are infected with flu.
And since the Aug. 9 CDC teleconference, scores of new human cases have been identified, in a lengthening list of states.
On Monday, Minnesota joined Wisconsin, West Virginia, Pennsylvania, Ohio, Michigan, Maryland, Indiana, Illinois and Hawaii to report human cases in the past month. Cases were also seen last year and this spring in Maine, Iowa and Utah.
"I think veterinary public health and human public health have done far too much to reassure the public that the methods taken at the fairs are going to substantially impact this transmission," says Osterholm.
"I think we have to be up front and honest about that. Does this mean this is potentially significant public health event? We don't know that. We have to be careful."
"I'm not sitting here crying 'wolf' or 'fire'. But at the same time, we can't reassure people that this is going to be an uneventful situation. We don't know."
So far the virus has not been found in pigs in Canada; no human cases have cropped up here either.
There are suspicions about that south of the border, given the degree of movement of pigs between the two countries. But a senior official with the Canadian Food Inspection Agency insists there has been no sign of the virus here.
Dr. Jim Clark, the agency's national manager of animal welfare, biosecurity and assurance programs, says pigs coming into Canada — except if they are headed for slaughter — are quarantined for 30 days and are only released if they are healthy. U.S. pigs coming to Canada for slaughter go directly to those facilities and don't interact with Canadian swine herds.
Also, while late summer fairs — like the Canadian National Exhibition, now underway in Toronto — are popular in Canada, they generally don't have the swine exhibits that are prominent features of U.S. state and county fairs, Clark says.
Dr. John Spika of the Public Health Agency of Canada says both his agency and CFIA are planning to beef up surveillance for the virus.
"You almost have to assume that it's here in Canada, given that it's just across the border," says Spika, director general for the centre for immunization and respiratory infectious diseases at the Public Health Agency.
Spika says the National Microbiology Laboratory in Winnipeg has been randomly screening a proportion of flu samples looking for H3N2v. But federal officials are interested in doing some targeted surveillance, looking for infections in children with exposure to pigs.
The lack of cases in adults has led some flu experts to conclude that years of exposure to human H3N2 viruses may give adults some protection against this virus.
That's despite the fact that a recently published Canadian study showed only about a quarter of the population would have what are considered protective antibodies against the virus.
The work, led by Dr. Danuta Skowronski at the B.C. Centre for Disease Control, showed the highest rates of antibodies in adolescents and young adults. Young children and middle-aged people had little or no immunity, her study found.
The study is considered well done, and the largest to date on this issue. Still, people are looking at the ages of the cases and suggesting there may be some protection in adults that the tests Skowronski used can't measure. (The tests she used are the standard ones to look for protection against influenza.)
"The ultimate arbitrator of what's really going on is what you see in populations — you know, what in fact is the infection pattern," says Dr. Keiji Fukuda, the senior influenza expert at the World Health Organization in Geneva.
"So why are we not seeing infections occur through the entire age spectrum? Well, the answer may partly be well, we're missing them in older people," says Fukuda, the WHO's assistant director-general for health security and the environment.
"Or it may be that in fact . . . older people have protection, younger people have less protection — that's what's really being reflected."
Osterholm suggests Fukuda's first explanation needs further exploration before people can assume the second is true.
Since the link between state fairs and human cases of H3N2v was spotted, public health officials have been looking for infections in children who attend fairs. There may not be as much of an effort to find cases in adults, he says, a situation that would skew the picture of the cases.
"We have to be incredibly careful about assuming that these fairs are telling us what's happening with these viruses in two ways," Osterholm says.
"One is in terms of who's at risk. And second of all we have very limited data on human-to-human transmission. Absence of evidence is not evidence of absence."Suggest a correction